Metal oxide semiconductors are very common circuit elements in integrated circuits (ICs). As the semiconductor fabricating processes reach into a sub-micro level, high-k gate dielectrics/metal gates become important elements in metal oxide semiconductors. Usually, the high-k gate dielectric and the metal gate are formed after finishing a self-aligned silicidation process for forming metal silicide layers on source/drain electrodes. However, metal silicide layers formed by the self-aligned silicidation process usually can't endure high temperature, and thus easily be damaged by the high temperature environment in the process for forming the high k gate dielectric. To overcome this disadvantage, through contact self-aligned silicidation process is developed.
In short, through contacts above the source/drain electrodes are firstly formed, and then self-aligned silicidation process is performed using the exposed through contacts as self-aligned mask and the reactants for producing the metal silicide layer can be intruded onto the source/drain electrodes from the through contacts. This process is the so-called through contact self-aligned silicidation process. However, as the size of semiconductors are becoming smaller and smaller, a diameter of the through contacts also becomes smaller and smaller. As a result, the silicidation process is very difficult to implement in the through contacts. Accordingly, the performance of metal oxide semiconductors is difficult to improve. Therefore, there is a desire to overcome the aforementioned disadvantages.